Provision of time information to a wireless device

ABSTRACT

There is provided provision of timing information of a first timing information source using timing information of a second timing information source to a wireless device. A network node determines that second timing information from the second timing information source is available and that timing information from the first timing information source is derivable from the second timing information. The network node instructs the wireless device to use the second timing information as a source for deriving first timing information of the first timing information source.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/441,273 filed 14 Jun. 2019, which is a continuation of U.S.application Ser. No. 16/202,736 filed 28 Nov. 2018 and now issued asU.S. Pat. No. 10,362,537, which is a continuation of U.S. applicationSer. No. 15/320,826 filed 21 Dec. 2016 and now issued as U.S. Pat. No.10,172,084, which is a U.S. National Phase Application ofPCT/EP2014/063871 filed 30 Jun. 2014. The entire contents of eachaforementioned application is incorporated herein by reference.

TECHNICAL FIELD

Embodiments presented herein relate to provision of time information toa wireless device, and particularly to a method, a network node, acomputer program, and a computer program product for providing timinginformation to a wireless device, and a method, a wireless device, acomputer program, and a computer program product for acquiring timinginformation.

BACKGROUND

In communications networks, there may be a challenge to obtain goodperformance and capacity for a given communications protocol, itsparameters and the physical environment in which the communicationsnetwork is deployed.

For example, one parameter in providing good performance and capacityfor a given communications protocol in a communications network is theavailability of accurate system time information.

For example, accurate system time information may be required inradio-based communications networks in order to facilitate good sleepopportunities for both wireless devices and network nodes, savingsignificant power on both sides, without introducing any ambiguities inthe communication links between the wireless devices and the networknodes. In general terms, time information is to the wireless deviceprovided by the network node in the serving cell of the wireless device.By maintain per cell time information the need to synchronize cells isremoved, simplifying deployment of radio-based communications networks.

Time information is provided in system broadcasts and the frequency andgranularity of the information is a trade-off between sleep efficiencyof the wireless devices, the maximum sleep time of the wireless devices,and system overhead. For example, in telecommunications networks basedon the long term evolution (LTE) standards the system frame number isprovided in the master information block (MIB) which is transmitted onceevery 10 ms. The time granularity is 10.24 seconds, or 1024 frames,limited by the number of bits used in the MIB to signal the framenumber.

It has been considered to extend the time information in communicationsnetworks to enable longer sleep-times for the wireless device, forexample by reserving additional bits for signaling or to introduce newmessages for providing a secondary timing, differentiating betweencycles of the existing timing.

However, in some communications networks, such as in some multi-layermulti technology environments, the ability of network energy saving bynetwork node dormancy and overhead saving is reduced by the need toprovide frequent time-information to enable efficient sleep of thewireless devices. The network node still frequently needs to providetime information in order for the wireless device to quickly(re-)acquire timing information.

Hence, there is still a need for an improved provision of timeinformation to a wireless device.

SUMMARY

An object of embodiments herein is to provide improved provision of timeinformation to a wireless device.

According to a first aspect there is presented a method for providingtiming information of a first timing information source using timinginformation of a second timing information source to a wireless device.The method is performed by a network node. The method comprisesdetermining that second timing information from the second timinginformation source is available and that timing information from thefirst timing information source is derivable from the second timinginformation. The method comprises instructing the wireless device to usethe second timing information as a source for deriving first timinginformation of the first timing information source.

Advantageously this enables efficient provision of time information tothe wireless device.

Advantageously this enables for long sleep-time in the wireless deviceand network nodes while reducing the overhead from providing timinginformation in the communications network.

According to a second aspect there is presented a network node forproviding timing information of a first timing information source usingtiming information of a second timing information source to a wirelessdevice. The network node comprises a processing unit. The processingunit is configured to determine that second timing information from thesecond timing information source is available and that timinginformation from the first timing information source is derivable fromthe second timing information. The processing unit is configured toinstruct the wireless device to use the second timing information as asource for deriving first timing information of the first timinginformation source.

According to a third aspect there is presented a computer program forproviding timing information of a first timing information source usingtiming information of a second timing information source to a wirelessdevice, the computer program comprising computer program code which,when run on a processing unit, causes the processing unit to perform amethod according to the first aspect.

According to a fourth aspect there is presented a method for acquiringtiming information of a first timing information source using timinginformation of a second timing information source. The method isperformed by a wireless device. The method comprises receivinginstructions from a network node to use second timing information of thesecond timing information source as a source for deriving first timinginformation of the first timing information source. The method comprisesreceiving the second timing information from the second timinginformation source.

According to a fifth aspect there is presented a wireless device foracquiring timing information of a first timing information source usingtiming information of a second timing information source. The wirelessdevice comprises a processing unit. The processing unit is configured toreceive instructions from a network node to use second timinginformation of the second timing information source as a source forderiving first timing information of the first timing informationsource. The processing unit is configured to receive the second timinginformation from the second timing information source.

According to a sixth aspect there is presented a computer program foracquiring timing information of a first timing information source usingtiming information of a second timing information source, the computerprogram comprising computer program code which, when run on a processingunit, causes the processing unit to perform a method according to thefourth aspect.

According to a seventh aspect there is presented a computer programproduct comprising a computer program according to at least one of thethird aspect ad the sixth aspect and a computer readable means on whichthe computer program is stored.

It is to be noted that any feature of the first, second, third, fourth,fifth, sixth and seventh aspects may be applied to any other aspect,wherever appropriate. Likewise, any advantage of the first aspect mayequally apply to the second, third, fourth, fifth, sixth, and/or seventhaspect, respectively, and vice versa. Other objectives, features andadvantages of the enclosed embodiments will be apparent from thefollowing detailed disclosure, from the attached dependent claims aswell as from the drawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, withreference to the accompanying drawings, in which:

FIGS. 1a and 1b are schematic diagrams illustrating a communicationsnetwork according to embodiments;

FIG. 2a is a schematic diagram showing functional units of a networknode according to an embodiment;

FIG. 2b is a schematic diagram showing functional modules of a networknode according to an embodiment;

FIG. 3a is a schematic diagram showing functional units of a wirelessdevice according to an embodiment;

FIG. 3b is a schematic diagram showing functional modules of a wirelessdevice according to an embodiment;

FIG. 4 shows one example of a computer program product comprisingcomputer readable means according to an embodiment;

FIGS. 5, 6, 7, and 8 are flowcharts of methods according to embodiments;

FIGS. 9 and 10 are signalling diagrams according to embodiments; and

FIG. 11 schematically illustrates timing information according to anembodiment.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe inventive concept are shown. This inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the inventive concept tothose skilled in the art. Like numbers refer to like elements throughoutthe description. Any step or feature illustrated by dashed lines shouldbe regarded as optional.

FIG. 1a is a schematic diagram illustrating a communications network 10a where embodiments presented herein can be applied. The communicationsnetwork 10 a comprises radio transceiver devices 11 a, 11 b in the formof network nodes (NNs). The network nodes may be provided as anycombination of radio access network nodes such as base transceiverstations (BTSs), Node Bs, Evolved Node Bs, or access points, such asaccess points for Wi-Fi. The radio transceiver devices 11 a, 11 b inFIG. 1a are configured to provide network coverage in cells 16 a, 16 bto a radio transceiver device 12 in the form of a wireless device (WD).The wireless device may be a portable wireless transceiver device, suchas a mobile phone, a smartphone, a tablet computer, a laptop computer orthe like, or other type of user equipment (UE) or Wi-Fi device. Withinthe cells 16 a, 16 b the radio transceiver devices 11 a, 11 b thus actas radio base stations for the radio transceiver device 12. The radiotransceiver devices 11 a, 11 b and the radio transceiver device 12 areconfigured to be operatively connected via wireless links 15 a, 15 b.The communications network 10 a further comprises a core network 13. Theradio transceiver devices 11 a, 11 b are operatively connected to thecore network 13. The core network 13 is in turn operatively connected toan Internet Protocol (IP) based service network 14. The radiotransceiver device 12 is thereby enabled to access content and servicesas provided by the IP based service network 14 via the wireless links 15a, 15 b.

FIG. 1b is a schematic diagram illustrating a communications network 10b where embodiments presented herein can be applied. The communicationsnetwork 10 b is similar to the communications network 10 a of FIG. 1aand comprises a radio transceiver device 11 in the form of a networknode 11 a configured to provide network coverage to a radio transceiverdevice 12 in the form of a wireless device. The radio transceiver device11 a is configured to provide network coverage in cells 16 a, 16 b, forexample using different radio access technologies. Hence, the radiotransceiver device 11 a may alternatingly in time or frequency or at thesame time and/or frequency act as a base transceiver station (BTS), aNode B, an Evolved Node B, and an access point. The communicationsnetwork 10 b further comprises a core network 13 as disclosed withreference to FIG. 1a and a service network 14 as disclosed withreference to FIG. 1 a.

Each network node 11 a, 11 b comprises a timing information source 17 a,17 b and is configured to provide timing information to the wirelessdevice 12. In the example of FIG. 1a the network node 11 a comprises afirst timing information source 17 a and the network node 11 b comprisesa second timing information source 17 b. In the example of FIG. 1b thenetwork node 11 a comprises a first timing information source 17 a and asecond timing information source 17 b. The timing information mayrepresent system time information in the communications network 10 a, 10b. At least some of the herein disclosed embodiments enable a networknode 11 a (or timing information source) of a first cell 16 a to informa wireless device 12 about timing information of a second cell 16 band/or a network node 11 a (or timing information source) of a firstcell 16 a to provide the wireless device 12 with information about asecond cell 16 b that can provide timing information to the wirelessdevice 12 of the first cell 16 a. At least some of the herein disclosedembodiments enable a wireless device 12 to utilize this information toderive timing for monitoring a downlink channel and to improve its sleeptime.

The embodiments disclosed herein particularly relate to timinginformation related to a wireless device. In order to provide timinginformation of a first timing information source using timinginformation of a second timing information source to a wireless devicethere is provided a network node, a method performed by the networknode, a computer program comprising code, for example in the form of acomputer program product, that when run on a processing unit of thenetwork node, causes the network node to perform the method. In order toacquire timing information of a first timing information source usingtiming information of a second timing information source there isfurther provided a wireless device, a method performed by the wirelessdevice, a computer program comprising code, for example in the form of acomputer program product, that when run on a processing unit of thewireless device, causes the wireless device to perform the method.

FIG. 2a schematically illustrates, in terms of a number of functionalunits, the components of a network node 11 a according to an embodiment.A processing unit 21 is provided using any combination of one or more ofa suitable central processing unit (CPU), multiprocessor,microcontroller, digital signal processor (DSP), application specificintegrated circuit (ASIC), field programmable gate arrays (FPGA) etc.,capable of executing software instructions stored in a computer programproduct 41 a (as in FIG. 4), e.g. in the form of a storage medium 23.Thus, the processing unit 21 is thereby arranged to execute methods asherein disclosed. The storage medium 23 may also comprise persistentstorage, which, for example, can be any single one or combination ofmagnetic memory, optical memory, solid state memory or even remotelymounted memory. The network node 11 a may further comprise acommunications interface 22 for communications with another network node11 b, the core network 13, and at least one wireless device 12. As suchthe communications interface 22 may comprise one or more transmittersand receivers, comprising analogue and digital components and a suitablenumber of antennas for radio communications and a suitable number ofports for wired communications. The processing unit 21 controls thegeneral operation of the network node 11 a e.g. by sending data andcontrol signals to the communications interface 22 and the storagemedium 23, by receiving data and reports from the communicationsinterface 22, and by retrieving data and instructions from the storagemedium 23. Other components, as well as the related functionality, ofthe network node 11 a are omitted in order not to obscure the conceptspresented herein.

FIG. 2b schematically illustrates, in terms of a number of functionalmodules, the components of a network node 11 a according to anembodiment. The network node 11 a of FIG. 2b comprises a number offunctional modules; a determine module 21 a, and an instruct module 21b. The network node 11 a of FIG. 2b may further comprises a number ofoptional functional modules, such as any of a provide module 21 c, anotify module 21 d, a send and/or receive module 21 e, and a checkmodule 21 f. The functionality of each functional module 21 a-f will befurther disclosed below in the context of which the functional modules21 a-f may be used. In general terms, each functional module 21 a-f maybe implemented in hardware or in software. Preferably, one or more orall functional modules 21 a-f may be implemented by the processing unit21, possibly in cooperation with functional units 22 and/or 23. Theprocessing unit 21 may thus be arranged to from the storage medium 23fetch instructions as provided by a functional module 21 a-f and toexecute these instructions, thereby performing any steps as will bedisclosed hereinafter.

FIG. 3a schematically illustrates, in terms of a number of functionalunits, the components of a wireless device 12 according to anembodiment. A processing unit 31 is provided using any combination ofone or more of a suitable central processing unit (CPU), multiprocessor,microcontroller, digital signal processor (DSP), application specificintegrated circuit (ASIC), field programmable gate arrays (FPGA) etc.,capable of executing software instructions stored in a computer programproduct 41 b (as in FIG. 4), e.g. in the form of a storage medium 43.Thus, the processing unit 31 is thereby arranged to execute methods asherein disclosed. The storage medium 33 may also comprise persistentstorage, which, for example, can be any single one or combination ofmagnetic memory, optical memory, solid state memory or even remotelymounted memory. The wireless device 12 may further comprise acommunications interface 32 for communications with at least one networknode 11 a, 11 b. As such the communications interface 32 may compriseone or more transmitters and receivers, comprising analogue and digitalcomponents and a suitable number of antennas for radio communications.The processing unit 31 controls the general operation of the wirelessdevice 12 e.g. by sending data and control signals to the communicationsinterface 32 and the storage medium 33, by receiving data and reportsfrom the communications interface 32, and by retrieving data andinstructions from the storage medium 33. Other components, as well asthe related functionality, of the wireless device 12 are omitted inorder not to obscure the concepts presented herein.

FIG. 3b schematically illustrates, in terms of a number of functionalmodules, the components of a wireless device 12 according to anembodiment. The wireless device 12 of FIG. 3b comprises a send and/orreceive module 31 a. The wireless device 12 of FIG. 3b may furthercomprises a number of optional functional modules, such as any of a usemodule 31 b, a determine module 31 c, and a request module 31 d. Thefunctionality of each functional module 31 a-d will be further disclosedbelow in the context of which the functional modules 31 a-d may be used.In general terms, each functional module 31 a-d may be implemented inhardware or in software. Preferably, one or more or all functionalmodules 31 a-d may be implemented by the processing unit 31, possibly incooperation with functional units 32 and/or 33. The processing unit 31may thus be arranged to from the storage medium 33 fetch instructions asprovided by a functional module 31 a-d and to execute theseinstructions, thereby performing any steps as will be disclosedhereinafter.

FIG. 4 shows one example of a computer program product 41 a, 41 bcomprising computer readable means 43. On this computer readable means43, a computer program 42 a can be stored, which computer program 42 acan cause the processing unit 21 and thereto operatively coupledentities and devices, such as the communications interface 22 and thestorage medium 23, to execute methods according to embodiments describedherein. The computer program 42 a and/or computer program product 41 amay thus provide means for performing any steps as herein disclosed. Onthis computer readable means 43, a computer program 42 b can be stored,which computer program 42 b can cause the processing unit 31 and theretooperatively coupled entities and devices, such as the communicationsinterface 32 and the storage medium 33, to execute methods according toembodiments described herein. The computer program 42 b and/or computerprogram product 41 b may thus provide means for performing any steps asherein disclosed.

In the example of FIG. 4, the computer program product 41 a, 41 b isillustrated as an optical disc, such as a CD (compact disc) or a DVD(digital versatile disc) or a Blu-Ray disc. The computer program product41 a, 41 b could also be embodied as a memory, such as a random accessmemory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM), or an electrically erasable programmableread-only memory (EEPROM) and more particularly as a non-volatilestorage medium of a device in an external memory such as a USB(Universal Serial Bus) memory. Thus, while each computer program 42 a,42 b is here schematically shown as a track on the depicted opticaldisk, the computer program 42 a, 42 b can be stored in any way which issuitable for the computer program product 41 a, 41 b.

FIGS. 5 and 6 are flow chart illustrating embodiments of methods forproviding timing information of a first timing information source usingtiming information of a second timing information source to a wirelessdevice as performed by the network node 11 a. FIGS. 7 and 8 are flowchart illustrating embodiments of methods for acquiring timinginformation of a first timing information source using timinginformation of a second timing information source as performed by thewireless device 12. The methods are advantageously provided as computerprograms 42 a, 42 b.

Network Node

Reference is now made to FIG. 6 illustrating a method for providingtiming information of a first timing information source 17 a usingtiming information of a second timing information source 17 b to awireless device 12 as performed by a network node 11 a according to anembodiment. Parallel references are made to the signalling diagrams ofFIGS. 9 and 10.

The network node 11 a in a step S104 determines that second timinginformation from the second timing information source 17 b is available.The network node 11 a in step S104 further determines that timinginformation from the first timing information source 17 a is derivablefrom the second timing information. The network node 11 a may beconfigured to perform step S104 by the processing unit 21 executingfunctionality of the determine module 21 a. The computer program 42 aand/or computer program product 41 a may thus provide means for thisstep.

The network node 11 a in a step S106 instructs the wireless device 12 touse the second timing information as a source for deriving the timinginformation of the first timing information source 17 a. The networknode 11 a may be configured to perform step S106 by the processing unit21 executing functionality of the instruct module 21 b. The computerprogram 42 a and/or computer program product 41 a may thus provide meansfor this step.

This enables a timing information source of one cell 16 a to providetime information to a wireless device 12 in a second cell 16 b, and bydoing so enable the wireless device 12 to save power. This also enablesoverhead in the communications network 10 a, 10 b in an area wherecoverage already exist from a second timing information source to bereduced.

Reference is now made to FIG. 7 illustrating methods for providingtiming information of a first timing information source 17 a usingtiming information of a second timing information source 17 b to awireless device 12 as performed by a network node 11 a according tofurther embodiments. Parallel references are continued to the signallingdiagrams of FIGS. 9 and 10.

The timing information provided by the first timing information source17 a and the second timing information source 17 b may represent systemtime information in the communications network 10 a, 10 b. The secondtiming information may be provided on a separate (dedicated) carrierfrequency. Further details of the timing information will be providedbelow.

There may be different ways for the network node 11 a to acquire theinformation that the second timing information is available. Accordingto one general embodiment the information that the second timinginformation is available is acquired from the wireless device. Accordingto one general embodiment the information that the second timinginformation is available is acquired from the second timing informationsource 17 b. According to one general embodiment the information thatthe second timing information is available is acquired from a networknode 11 b of the second timing information source 17 b.

There may be different types of timing information sources 17 a, 17 b.According to one general embodiment the first timing information source17 a is a timing information source of a first cell 16 a. According toone general embodiment the second timing information source 17 b is atiming information source of a second cell 16 b. The first cell 16 a andthe second cell 16 b may be served by the same network node 11 a. Hencethe first timing information source 17 a and the second timinginformation source 17 b may be provided in the same network node 11 a.

The first cell 16 a may be a serving cell of the wireless device 12 whenthe network node 11 a instructs the wireless device 12 to use the secondtiming information as its source for timing information in step S106.

In some embodiments the first timing information source 17 a and thesecond timing information source 17 b are separable by having differentgeographical coverage area, be transmitted from separate points, such asfrom different network nodes 11 a, 11 b, be transmitted on differentcarrier frequencies and/or constitute different radio accesstechnologies. The first timing information source 17 a and the secondtiming information source 17 b may thus use the same or different radioaccess technologies (RATs) for transmitting timing information. Thefirst timing information source 17 a and the second timing informationsource 17 b may thus transmit in the same or different area. Hence thefirst timing information source 17 a and the second timing informationsource 17 b may have the same or different network coverage. The firsttiming information source 17 a and the second timing information source17 b may thus use the same or different carrier frequency fortransmitting timing information. Hence, according to one generalembodiment at least one of RAT, network coverage, and carrier frequencyof the first timing information source 17 a and the second timinginformation source 17 b is different. Hence, according to one generalembodiment the first timing information source 16 a share at least oneof RAT, network coverage, and carrier frequency with the second timinginformation source 17 b.

The network node 11 a may also provide timing information to thewireless device 12. Particularly, the network node 11 a may, in anoptional step S108, provide timing information of the first timinginformation source 17 a to the wireless device 12. The network node 11 amay be configured to perform step S108 by the processing unit 21executing functionality of the provide module 21 c. The computer program42 a and/or computer program product 41 a may thus provide means forthis step. The timing information of the first timing information source17 a and the timing information of the second timing information source17 b may by the wireless device 12 be used separately, complementary, orjoint. In some embodiments the network node 11 a notifies the wirelessdevice 12 served by the network node 11 a of the first timinginformation source 17 a to acquire a better time resolution by combiningtiming information from first timing information source 17 a and thesecond timing information source 17 b. Thus, the network node 11 a may,in an optional step S110, instruct the wireless device 12 to combine thetiming information of the second timing information source 17 b and thetiming information of the first timing information source 17 a. Thenetwork node 11 a may be configured to perform step S110 by theprocessing unit 21 executing functionality of the instruct module 21 b.The computer program 42 a and/or computer program product 41 a may thusprovide means for this step

In some embodiments a first timing information source 17 a providestiming information with a first resolution and a second cell timinginformation source 17 b provides timing information of a secondresolution, where resolution here refers to the time duration of atime-cycle in a first cell 16 a and a second cell 16 b, or the timebetween messages as issued by the first timing information source 17 aand the second timing information source 17 b indicating current systemtime. The timing information of the second timing information source 17b and the timing information of the first timing information source 17 amay thus have different resolution. This is illustrated in FIG. 11 (seebelow). For example, the timing information of the second timinginformation source 17 b may have higher resolution than the timinginformation of the first timing information source 17 a. This isillustrated in FIG. 11 (see below). The resolution may thus be definedby a time duration of a time-cycle or a time duration between twomessages indicating current system time.

In some embodiments the time granularity of the first timing informationsource 17 a and the second timing information source 17 b is the same,but the frequency of providing time information is different. In thiscase it may be sufficient to inform the wireless device 12 about arelation in time between the first timing information source 17 a andthe second timing information source 17 b. Further, the timinginformation of the second timing information source 17 b and the timinginformation of the first timing information source 17 a may thus havesame time granularity. A frequency of providing the timing informationof the second timing information source 17 b and the timing informationof the first timing information source 17 b may thus be different.

The total time cycle length of the timing information of the firsttiming information source 17 a may be different from the total cyclelength of the timing information of the second timing information source17 b. This is illustrated in FIG. 11 (see below). Thus, in someembodiments the total time cycle length of the first timing informationsource 17 a is different from the total cycle length of the secondtiming information source 17 b. If the difference in cycle length iskept a non-multiple of each other, the two timing information sources 17a, 17 b will drift in relation to each other in frame number in apredictable way, thereby enabling the timing information from the twotiming information sources 17 a, 17 b to be combined, thus enabling anextended time granularity to be determined. As an example, considertiming information sources 17 a, 17 b of two long term evolution (LTE)cells where the timing information source 17 b of one cell makes aslight intentional time-error such that the time-cycle of one cell is10.23 s while the other cell has a time-cycle of 10.24 s. This wouldeffectively scale up the granularity of the timing information up tomore than 100 s. A wireless device 12 may then be configured to monitorpaging in any radio-frame fulfilling its paging occasion in both cellssimultaneously, giving a significantly longer, but still deterministicpaging cycle.

Properties of the first timing information source 17 a and the secondtiming information source 17 b may be reported to the wireless device12. For example, the network node 11 a may, in an optional step S112,notify the wireless device 12 about a relation in time between thetiming information of the second timing information source 17 b and thetiming information of the first timing information source 17 a. Thenetwork node 11 a may be configured to perform step S112 by theprocessing unit 21 executing functionality of the notify module 21 d.The computer program 42 a and/or computer program product 41 a may thusprovide means for this step. In some embodiments the network node 11 anotifies the wireless device 12 about a maximum drift in time betweenthe first timing information source 17 a and the second timinginformation source 17 b. Thus, the network node 11 a may, in an optionalstep S114, notify the wireless device 12 about a drift in time betweenthe timing information of the first timing information source 17 a andthe timing information of the second timing information source 17 b. Thenetwork node 11 a may be configured to perform step S114 by theprocessing unit 21 executing functionality of the notify module 21 d.The computer program 42 a and/or computer program product 41 a may thusprovide means for this step.

There may be different reasons for the network node 11 a to determinethat second timing information from the second timing information source17 b is available, as in step S104. In some embodiments the wirelessdevice 12 reports to the network node 11 a in its serving cell if it hassufficient coverage from a second timing information source 17 b to useit for time reference. Thus, the determining in step S104 may betriggered by a request from the wireless device 12. Hence, the networknode 11 a may, in an optional step S102, receive a request from thewireless device 12 to provide timing information. The network node 11 amay be configured to perform step S102 by the processing unit 21executing functionality of the send and/or receive module 21 e. Thecomputer program 42 a and/or computer program product 41 a may thusprovide means for this step

The determining in step S104 and the instructing in step S106 may thenbe performed in response to the request being received by the networknode 11 a as in step S102. The network node 11 a may be configured tohandle the request received in step S102 based on at least one propertyof the wireless device 12 sending the request. One such property is asubscription. Particularly, the network node 11 a may, in an optionalstep S118, check a subscription criterion of the wireless device 12. Thenetwork node 11 a may be configured to perform step S118 by theprocessing unit 21 executing functionality of the check module 21 f. Thecomputer program 42 a and/or computer program product 41 a may thusprovide means for this step. The instructing in step S102 may then beperformed only if the subscription criterion is fulfilled. Thesubscription criterion may relate to a subscription to additional timinginformation (in addition to timing information as provided by the timinginformation source 17 a of the serving network node 11 a of the wirelessdevice 12). Hence the instructing in step S102 may be performed only ifthe wireless device 12 has a subscription to such additional timinginformation.

In some embodiments additional information is provided at thetime-occasions when timing information is provided, where thisadditional information provides information about the need for thewireless device 12 to in the following time period wake up and monitorfor scheduling. As an example, a signal which provides timinginformation of a specific granularity may be accompanied by a signalindication if the network node 11 a has any pending paging messages tobe delivered, to all or a subset of served wireless devices 12 until thenext occasion of a signal providing timing information of the samegranularity. This can be provided in a multi-step signaling approach,where timing information is provided on multiple levels of granularity.

In some embodiments additional resources may be configured by a networknode 11 a to provide timing information, for example in the case thatthe network node 11 a serves a wireless device 12 without coverage fromany second timing information source 17 b. The network node 11 a maythus, in an optional step S120, provide further timing information tothe wireless device 12. The network node 11 a may be configured toperform step S120 by the processing unit 21 executing functionality ofthe provide module 21 c. The computer program 42 a and/or computerprogram product 41 a may thus provide means for this step. This furthertiming information may be different from or identical to the timinginformation of the second timing information source 17 b. For example,the network node 11 a may, in an optional step S116, receive anindication from the wireless device 12 that the timing information ofthe second timing information source 17 b is not available. The networknode 11 a may be configured to perform step S116 by the processing unit21 executing functionality of the send and/or receive module 21 e. Thecomputer program 42 a and/or computer program product 41 a may thusprovide means for this step. The further timing information may then beprovided to the wireless device 12 in response thereto. For example, thewireless device 12 may be outside coverage 16 b of the second timinginformation source 17 b and hence not be able to directly receive anytiming information from the second timing information source 17 b. Thewireless device 12 may then request further timing information from thenetwork node 11 a. The further timing information may by the networknode 11 a be provided to the wireless device 12 during a time intervalin which the wireless device 12 is configured to wake up and monitor forscheduling.

In some embodiments it is the second timing information source 17 b thatprovides the wireless device 12 with information about time informationfor the first timing information source 17 a. This information may forexample be provided in system broadcast where the second timinginformation source 17 b may point out one or multiple other cells, forwhich it can provide a time reference.

In some embodiments it is not a specific cell that is indicated but acarrier frequency, where any cell on the indicated carrier frequency canbe used for time reference or use this cell as time reference. Anexample of such a communications network is where a new radio accesstechnology that provides system information, and related timinginformation on a slow time-scale, e.g. by a broadcast message sent onesevery 10.24 second is added to an existing communications network. Ifthis new radio access technology is deployed in an area with at leastpartial existing network coverage, such as long term evolution (LTE)coverage, the wireless device 12 may be informed, from the network node11 a of the serving cell 16 a or from the LTE cell (as exemplified bycell 16 b), that these two cells share a timing relation, or a maximaltime drift. The wireless device 12 may then utilize this information towake up and monitor the time-information on the LTE cell, provided every10 ms, to correct its current clock-timing towards the serving cell 16a. This enables the wireless device 12 longer sleep-time and moreaccurate wake-up, thus saving power in the wireless device 12.

Wireless Device

Reference is now made to FIG. 8 illustrating a method for acquiringtiming information of a first timing information source 17 a usingtiming information of a second timing information source 17 b asperformed by a wireless device 12 according to an embodiment. Parallelreferences are continued to the signalling diagrams of FIGS. 9 and 10.

The wireless device 12 in a step S208 receives instructions from anetwork node 11 a to use second timing information of a second timinginformation source 17 b as a source for deriving first timinginformation of the first timing information source 17 b. The wirelessdevice 12 may be configured to perform step S208 by the processing unit31 executing functionality of the send and/or receive module 31 a. Thecomputer program 42 b and/or computer program product 41 a may thusprovide means for this step.

The wireless device 12 in a step S210 receives the second timinginformation from the second timing information source 17 b. The wirelessdevice 12 may be configured to perform step S210 by the processing unit31 executing functionality of the send and/or receive module 31 a. Thecomputer program 42 b and/or computer program product 41 a may thusprovide means for this step.

Reference is now made to FIG. 9 illustrating methods for acquiringtiming information of a first timing information source 17 a usingtiming information of a second timing information source 17 b asperformed by a wireless device 12 according to further embodiments.Parallel references are continued to the signalling diagrams of FIGS. 9and 10.

The wireless device 12 may, in an optional step S212, use the secondtiming information as its source for timing information. The wirelessdevice 12 may be configured to perform step S212 by the processing unit31 executing functionality of the use module 31 b. The computer program42 b and/or computer program product 41 a may thus provide means forthis step. There are different ways for the wireless device 12 to usethe second timing information as its source for timing information. Forexample, the wireless device may, in an optional step S214, determine,based on the second timing information, timing for when to transmit anuplink signal to the network node 11 a of the first timing informationsource 17 a. The wireless device 12 may be configured to perform stepS214 by the processing unit 31 executing functionality of the determinemodule 31 c. The computer program 42 b and/or computer program product41 a may thus provide means for this step. In some embodiments thewireless device 12 uses the provided timing information to e.g.calculate time occasions to monitor a downlink channel. Thus, thewireless device may, in an optional step S216, determine, based on thesecond timing information, timing for when to monitor a downlinkchannel. The wireless device 12 may be configured to perform step S216by the processing unit 31 executing functionality of the determinemodule 31 c. The computer program 42 b and/or computer program product41 a may thus provide means for this step.

As disclosed above, one reason for the network node 11 a to determinethat second timing information from the second timing information source17 b is available, as in step S104, is a request as received by thenetwork node 11 a, as in step S102, from the wireless device 12. Hence,the wireless device 12 may, in an optional step S202, request timinginformation from the network node 11 a of the first timing informationsource 17 a. The wireless device 12 may be configured to perform stepS202 by the processing unit 31 executing functionality of the requestmodule 31 d. The computer program 42 b and/or computer program product41 a may thus provide means for this step.

Further, the wireless device 12 may, in an optional step S204, determinethat the wireless device 12 has sufficient coverage 16 b from the secondtiming information source 16 b. The wireless device 12 may be configuredto perform step S204 by the processing unit 31 executing functionalityof the determine module 31 c. The computer program 42 b and/or computerprogram product 41 a may thus provide means for this step. The wirelessdevice 12 may then, in an optional step S206, send a report thereof tothe network node 11 a of the first timing information source 17 a. Thewireless device 12 may be configured to perform step S206 by theprocessing unit 31 executing functionality of the send and/or receivemodule 31 a. The computer program 42 b and/or computer program product41 a may thus provide means for this step. The network node 11 a maythen determine whether or not to instruct the wireless device 12 to usethe use the second timing information as its source for timinginformation.

As disclosed above, the network node 11 a may, in an optional step S116,receive an indication from the wireless device 12 that the timinginformation of the second timing information source 17 b is notavailable. In some embodiments there may thus be occasions where thewireless device 12 does not have sufficient coverage from the secondtiming information source 17 b. This can however be detected by thewireless device 12 and may result in the wireless device 12 having tokeep track of the timing information provided by the network node 11 ofits serving cell. This would remove the power saving opportunity forthis specific wireless device 12 but not break the system operation.Therefore, the wireless device 12 may, in an optional step S218,determine that the wireless device 12 does not have sufficient coverage16 b from the second timing information source 17 b. The wireless device12 may be configured to perform step S218 by the processing unit 31executing functionality of the determine module 31 c. The computerprogram 42 b and/or computer program product 41 a may thus provide meansfor this step. The wireless device 12 may then, in an optional stepS220, send a report thereof to the network node 11 a of the first timinginformation source 17 a. The wireless device 12 may be configured toperform step S220 by the processing unit 31 executing functionality ofthe send and/or receive module 31 a. The computer program 42 b and/orcomputer program product 41 a may thus provide means for this step. Thenetwork node 11 a may then determine whether or not to provide furthertiming information to the wireless device 12, as in step S120.

EXAMPLES

As an example, consider a wireless device 12 camping on a carrierfrequency in a serving cell 16 a that does not provide any timinginformation except for a periodic sync signal sent out with aperiodicity Psync of subframes. The timing information of the firsttiming information source 17 a may thus represent such as periodic syncsignal. On a separate carrier frequency, another cell 16 b covers thesame area providing time resolution of up to 10.24 s in CellBSFN, whereSFN is short for system frame number, and where CellB is the cell of thesecond timing information source 17 b. A wireless device 12 could thenderive a set of subframes (SF) to monitor a control channel as allsubframes fulfilling:SF mod Psync=n; andfloor(CellBSFN/k)*q mod 1024=m,where n, k, q and m are parameters (derived or configured) for thewireless device 12. Hence the set of subframes SF may be written asSF={all x; x mod Psync=n} and the set of possible SFN may be written asSFN={all y; floor(CellBy/k)*q mod 1024=m}, where CellBy is system framenumber y. Hence, SF is a subframe number in cell 16 a (using the firsttiming information source 17 a), and SFN is a subframe number in cell 16b (using the second timing information source 17 b). The subframemonitoring would hence be done in SF number n of the serving cell 16 aof the wireless device 12, but only during time durations where thetiming information of the second timing information source 17 b fulfillssome condition.

FIG. 11 schematically illustrates an example of two timing informationsources 17 a, 17 b operating with different time information, where thefirst timing information source 17 has a larger maximum time and wherethe second timing information source 17 b provides more frequent timeinformation. As an example, a timing information system for providingsystem time to a wireless device 12 may be formed by multiple signals,e.g. one timing signal T1 sent every N subframes (as represented by thefirst timing information source 17 a in part (a) of FIG. 11) and asecond timing signal T2 sent every m*N subframes (as represented by thesecond timing information source 17 b in part (b) of FIG. 11), and soon. A wireless device 12 (as represented by the wireless device in part(c) of FIG. 11) waking up from a very long sleep time would first haveto locate the second timing signal T2 (at time t1 in FIG. 11) to findtiming information of needed granularity. After finding the T2 timinginformation the wireless device 12 may go back to sleep (at time t2 inFIG. 11) to wake up (at time t3 in FIG. 11) and find T1 to finally wakeup at the paging occasion (at time t4 in FIG. 11) relative T2 and T1 andthen go to sleep again (at time t5 in FIG. 11). The wireless device 12may also back to sleep again (at time t5 in FIG. 11) and skip the pagingoccasion if information that no paging is sending is received at theoccasion of T2 or T1 (e.g., at time t4 in FIG. 11).

The inventive concept has mainly been described above with reference toa few embodiments. However, as is readily appreciated by a personskilled in the art, other embodiments than the ones disclosed above areequally possible within the scope of the inventive concept, as definedby the appended patent claims.

What is claimed is:
 1. A method performed by a network node, the methodcomprising: determining that second timing information is available at awireless device and that timing of a first cell is derivable from thesecond timing information, wherein the second timing information isperiodically transmitted via a second cell, to indicate timing of thesecond cell; and instructing, via the second cell, the wireless deviceto derive the timing of the first cell using the second timinginformation, wherein System Frame Numbers (SFNs) indicated in the secondtiming information are usable by the wireless device to identifysubframes of the first cell to monitor for control-channel signaling;wherein the first and second cells are cells of one or more radio accessnetworks, and wherein the network node operates in at least one of theone or more radio access networks.
 2. The method according to claim 1,further comprising determining that the second timing information isavailable at the wireless device, based on information acquired from thewireless device.
 3. The method according to claim 1, further comprisingdetermining that the second timing information is available at thewireless device, based on information acquired from the second cell. 4.The method according to claim 1, wherein the instructing includesproviding instructions for the wireless device to derive the timing ofthe first cell using the second timing information at least duringintervals between the first cell periodically transmitting first timinginformation that indicates the timing of the first cell.
 5. The methodaccording to claim 1, wherein the first cell is a serving cell of thewireless device.
 6. The method according to claim 1, wherein at leastone of radio access technology, network coverage, and carrier frequencyof the first cell and the second cell is different.
 7. The methodaccording to claim 1, wherein the first cell shares at least one ofradio access technology, network coverage, and carrier frequency withthe second cell.
 8. A method performed by a wireless device, the methodcomprising: receiving instructions, via a second cell, to use secondtiming information to derive timing of a first cell, wherein the firstand second cells are cells of one or more radio access networks and thesecond timing information is periodically transmitted via the secondcell and indicates timing of the second cell; receiving the secondtiming information from the second cell; deriving the timing of thefirst cell using the second timing information; determining a set ofsubframes to monitor for control channel transmissions in the firstcell, based on the timing of the first cell, as derived from the secondtiming information; and determining System Frame Numbers (SFNs) for thefirst cell based on SFN indications received in the second timinginformation from the second cell.
 9. The method according to claim 8,wherein the instructions instruct the wireless device to derive thetiming of the first cell using the second timing information at leastduring intervals between periodic transmissions, by the first cell, offirst timing information that indicates the timing of the first cell.10. The method according to claim 8, wherein a carrier frequency of thefirst cell is different from a carrier frequency of the second cell. 11.A network node that comprises: communication circuitry configured forcommunication with a wireless device or with another node that isconfigured for communication with the wireless device; and processingcircuitry operatively associated with the communication circuitry andconfigured to: determine that second timing information is available atthe wireless device and that timing of a first cell is derivable fromthe second timing information, wherein the second timing information isperiodically transmitted via a second cell, to indicate timing of thesecond cell; and instruct, via the second cell, the wireless device toderive the timing of the first cell using the second timing information,wherein System Frame Numbers (SFNs) indicated in the second timinginformation are usable by the wireless device to identify subframes ofthe first cell to monitor for control-channel signaling; and wherein thefirst and second cells are cells of one or more radio access networks,and wherein the network node is configured for operation in associationwith at least one of the one or more radio access networks.
 12. Awireless device comprising: communication circuitry configured forcommunication with one or more radio access networks; and processingcircuitry operatively associated with the communication circuitry andconfigured to: receive instructions, via a second cell, to use secondtiming information to derive timing of a first cell, wherein the firstand second cells are cells of the one or more radio access networks, andwherein the second timing information is periodically transmitted viathe second cell and indicates timing of the second cell; receive thesecond timing information from the second cell; derive the timing of thefirst cell using the second timing information; determine a set ofsubframes to monitor for control channel transmissions in the firstcell, wherein the determining the set of subframes to monitor is basedon the timing of the first cell, as derived from the second timinginformation; and determine System Frame Numbers (SFN) for the first cellbased on SFN indications received in the second timing information fromthe second cell.
 13. The wireless device according to claim 12, whereinthe processing circuitry is configured to control the wireless deviceto: camp on a downlink carrier of the first cell that provides aperiodic synchronization signal with a first periodicity; and maintainsynchronization with the downlink carrier during intervals betweentransmission of the periodic synchronization signal using the secondtiming information, which is transmitted with a shorter periodicity thanthe periodic synchronization signal.